After a week of devastating flooding, which washed out roadways and destroyed buildings, Colorado residents are now facing the threat of contaminated waters, AccuWeather.com reported Wednesday.

The northeastern corner of Colorado, which contains numerous gas and oil wells and active drilling sites, has been inundated with rushing water.

Gary Wockner, Colorado program director for Clean Water Action, said it will take days for the flood waters to recede enough to assess the contamination damage adequately.

"Once those chemicals hit flood water, they get across a large swath of the landscape," Wockner said. "Our big concern is oil and gas and fracking chemicals in the water. We have seen photos of oil slicks on top of the floodwaters and we are continuing to monitor all of the flooding and cleanup efforts. Oil, gas and fracking chemicals are poisonous to people and animals, and could pollute farms and drinking water supplies."

He said that at least 1,000 gas wells have reportedly been flooded. The Denver Business Journal reported that at least two storage tanks were found floating in flood waters. In Weld County alone, where significant flooding has taken place, has more than 18,000 gas and oil wells.

Water treatment and sewage centers have also been flooded, which had led to advisories to boil water in some mountain communities where the initial surge took place. But boiling won't clean water in areas that may have been affected by leaked fracking chemicals or gas and oil well overflows. Wockner said the best way to avoid the health hazards associated with these containments is to drink filtered tap or bottled water.

The Environmental Protection Agency responded to questions about their involvement in surveying the contamination risks, stating that they are "beginning to assess water quality impacts from various sources, including oil and gas production."

The EPA is working with the Federal Emergency Management Agency, state and local resources to assess how the flooding has impacted drinking water and waste water.

Colorado residents were asked to continue to taking precautions against the possibility of West Nile virus, due to the increased rainfall and flooding. Low levels of virus activity in Colorado commonly continue through September and into October, Boulder officials said.

Six dead

The flooding has claimed six lives, Colorado Department of Emergency Management spokeswoman Micki Trost confirmed to AccuWeather.com. The death toll was as high as eight people, but two people on the list from Larimer County who were presumed dead are now considered as missing.

Less than 500 people remained unaccounted for as of 7 p.m. EDT Tuesday, Trost said.

American Red Cross Volunteer and Public Information Officer Larry Fortmuller is on the ground in Colorado, receiving people who are being airlifted to Red Cross shelters. At the shelters, people are provided with clean bottled water, food, health care, mental health care and access to computers to connect with loved ones. They have been reuniting families and helping to take care of those people who have no where to go.

On Sept. 16, the Fort Collins, Colo. Red Cross center where Fortmuller is working received more than 300 people and 200 pets. He said helicopters were able to run for only half a day because of rain and cloud cover, but after the rain stopped on Tuesday, they were expecting to bring in even more people.

According to AccuWeather.com Meteorologist Kristina Pydynowski, Colorado conditions will improve for rescue efforts throughout the week. Stray shower may pass through later in the day on Wednesday. These passing showers or thunderstorms should not be persistent or heavy, however. Skies will remain partly sunny but will clear up significantly after Thursday morning. It should stay clear and dry through to most of Sunday.

"I've heard it over and over again, people who say 'I never thought it would happen to us,'" Fortmuller said. "I heard it in Moore, I heard it in Boston, I heard it following Sandy. Nobody expects to need the Red Cross to come to their community."

Because of the breadth of the affected area in Colorado, the Red Cross is requiring supplies "by the truckload."

"It's only a 10-minute helicopter ride to the emergency shelters, but when you have no food, no water, no electricity... it's tough," Fortmuller said of those still stranded in the disaster area. He said many people are unable to use their cell phones and are "really isolated" as they wait for rescue.